Exercise treadmills are now widely used in gymnasiums, spas, clinics and private homes for aerobic exercise, physical examinations and physical therapy, for instance, during recovery from a cardiac illness. An exercise treadmill in its simplest form includes an endless belt that moves over an underlying support composed of a series of rollers or a flat bed. The belt is powered either by the walker's or runner's feet, or by an electric motor. Not uncommonly, exercise treadmills now employ microcomputers that control the speed of the drive motor, monitor and individual's workout, and display various workout parameters, such as time, speed, distance traveled, and calories expanded.
An advancement which has been made to render exercise treadmills more versatile is to position the treadmill at various angles of inclination to simulate walking or running up a grade or down a grade. Various mechanisms have been employed to raise and lower the front end of an exercise treadmill relative to the floor or other support surface on which the treadmill is positioned. Systems for manually changing the inclination of the treadmill are disclosed by U.S. Pat. Nos. 931,394, 2,117,957, 4,151,988, 4,591,147 (assigned to the assignee of the present application), Nos. 4,602,799 and 4,664,371. Powered or motorized systems for adjusting the inclination of treadmills are disclosed by U.S. Pat. Nos. 3,643,943, 4,363,480, 4,643,418; West German Pat. No. 3,601,184 and United Kingdom Pat. No. 2,152,825.
A serious problem associated with running or jogging stems from the shock forces that are imparted on the feet, ankles and knees of the runner upon impact of the runner's feet on the track, pavement, treadmill deck or other unyielding surface. This problem has been addressed in a few prior art treadmill designs. For example, U.S. Pat. No. 2,399,915 discloses an exercise treadmill having an endless belt trained around a forward drive drum and a rear idler drum, both mounted on the ground engaging frame of the treadmill. The drive drum is connected to an electric motor. The belt is supported by a series of underlying transverse rollers mounted on a platform. The ends of the roller platform are supported by shock absorbers which allow the platform to yield under the loads imposed by the runner's feet.
U.S. Pat. No. 4,350,336 discloses motorized exercise treadmill having an underlying frame structure for supporting an endless belt trained over a forward drive roller and a rear idler roller, both mounted on the underlying frame. The upper run of the endless belt is supported by a platform composed of individual rails pivotally connected at their rear ends to the underlying frame. The forward ends of the rails are supported by rubber blocks which can be moved along the length of the rails.
U.S. Pat. No. 3,689,066 discloses a third type of shock absorbing treadmill wherein an endless belt is trained over a drive drum and idler drum both mounted on an underlying frame structure. The upper run of the endless belt is supported by a number of bellows cells mounted on an underlying ridged base plate.
The foregoing attempts to reduce the shock forces imposed on the runner utilizing the treadmill suffer from serious drawbacks. For instance, in each instance the structure for supporting the upper run of the belt is mounted in the resilient manner, but the endless belt itself is not. Rather, the drive roller and idler rollers at the ends of the endless belt are both mounted directly on the underlying frame. As a result, the belt must run over the belt support structure with sufficient slack to allow the underlying support structure to move downwardly in response to the impact of the runner's foot. This slack can cause the belt to present an uneven lateral surface for succeeding foot landings, perhaps leading to twisted ankles and knees or other injuries.
In addition, the level of resistance imparted by the belt support systems disclosed in the foregoing patent references is substantially constant throughout the downward movement or deflection of the belt support structure. The reaction force imposed on the runner, though less than if the belt were not supported by a resilient system, remains very significant. Thus, a substantial level of shock is still transmitted through the feet, ankles and legs of the runner.